Low noise address line repair method for thin film imager devices

ABSTRACT

A method of repairing an open circuit defect in a damaged address line in a thin film electronic imager array is provided that includes the steps of forming a repair area exposing the open circuit defect and portions of the damaged address line adjoining the defect, with a first protective layer disposed over the array surrounding the repair area; depositing a layer of conductive repair material over the array so that a portion of the conductive repair material is disposed in the repair area to form a repair shunt electrically connecting the portions of the address line adjoining the defect; forming a planarized second protective layer over the array; removing portions of the second protective layer to form a planarized surface on the array on which the conductive repair material is exposed except for the repair shunt underlying a plug portion of the second protective layer disposed over the repair area; removing the conductive repair material from the array surface except for the portion underlying the plug portion of the second protective layer; and removing remaining portions of the first protective layer and the second protective layer plug portion from the repair area.

BACKGROUND OF THE INVENTION

This invention relates generally to thin film electronic imager devicesand more particularly to repair of address line structures contained indevices such as solid state radiation imagers having a matrix ofelectrically conductive address lines for controlling the activecomponents of the device.

Address lines for conducting electrical signals to and from activecomponents in a display or imager device are formed as integral parts ofthe structure of solid state imagers. These address lines usually form amatrix, with lines running in one direction designated as scan lines andlines disposed in a substantially perpendicular direction designated asdata lines. Electrical signals (e.g. the voltage) on a scan linetypically control a switching device, such as a field effect transistor(FET, also referred to as a thin film transistor, or TFT), that in turncouples the active component, such as a photosensor, to the data line sothat an electrical signal from the photosensor can be read out. A commonelectrode is disposed over the photosensor array to provide the commoncontact for each photosensor pixel in the array. The electrical signalthat is read out corresponds to the number of detected photons incidenton the array, and the signals from the respective photosensors are usedto electronically reproduce an image of the photons detected by thearray of photosensors.

A defect on a data line can adversely affect overall performance of thethin film imager device. This situation is particularly of concern inimagers in which the data lines have been severed in the middle of thearray in order to reduce noise levels (so called "single contact" datalines, as such severed lines are necessarily connected to readoutelectronics on one side of the array). In this arrangement, it isnecessary to be able to read the data lines from each side (or edge) ofthe array, and an open circuit condition effectively disables all pixelsconnected to the address line beyond the point where the open circuitexists. Some degradation of the number of operative pixels can betolerated with appropriate software changes in the read out circuits;replacement of the pixel array (which would be anticipated during thelife of the imager), however, would necessarily require revision of thereadout software, increasing the time and expense of servicing of theimager. Further, an imager having sufficient defective address lines mayhave to be discarded, depending upon the degradation of the resolutionof the display device resulting from the inoperative pixels.

Given the expense of fabricating thin film electronic imager devices, itis desirable to have devices that are repairable. In particular, it isdesirable to have a device that is readily repaired without significantadditional processing time during fabrication. It is further desirablethat the repair process for data lines that have an open circuit defectbe such so as to not significantly increase the amount of electronicnoise on the conductive line while still providing repair that isrobust.

SUMMARY OF THE INVENTION

In accordance with this invention a method of repairing an open circuitdefect in a damaged address line in a thin film electronic imager arrayis provided that is performed at the point in the fabrication process atwhich the materials to form the thin film field effect transistors(FETs) and associated data address lines have been deposited andpatterned (the "FET complete" stage) and prior to the stage ofdepositing photosensor barrier layers over the array, such as organicand inorganic dielectric materials deposited after formation ofphotosensors coupled to respective FETs.

The method of this invention includes the steps of forming a repair areaexposing the open circuit defect and portions of the damaged addressline adjoining the defect, with a first protective layer disposed overthe array surrounding the repair area; depositing a layer of conductiverepair material over the array so that a portion of the conductiverepair material is disposed in the repair area to form a repair shuntelectrically connecting the portions of the address line adjoining thedefect; forming a planarized second protective layer over the array;removing portions of the second protective layer to form a planarizedsurface on the array on which the conductive repair material is exposedexcept for the repair shunt underlying a plug portion of the secondprotective layer disposed over the repair area; removing the conductiverepair material from the array surface except for the portion underlyingthe plug portion of the second protective layer; and removing remainingportions of the first protective layer and the second protective layerplug portion from the repair area.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the invention believed to be novel are set forth withparticularity in the appended claims. The invention itself, however,both as to organization and method of operation, together with furtherobjects and advantages thereof, may best be understood by reference tothe following description in conjunction with the accompanying drawingsin which like characters represent like parts throughout the drawings,and in which:

FIG. 1 is a plan view of a portion of a thin film electronic imagerarray having a damaged address line.

FIG. 2 is a cross-sectional view of the damaged imager array taken alongline I--I in FIG. 1 following deposition of a first protective layer andformation of a repair area over the defect in the address line inaccordance with this invention.

FIG. 3 is a cross-sectional view of the damaged imager array followingdeposition of the conductive repair material and second protective layerin accordance with the present invention.

FIG. 4 is a cross-sectional view of the damaged imager array in whichthe conductive repair material has been exposed except for the repairarea in accordance with the present invention.

FIG. 5 is a cross-sectional view of an imager array after completion ofthe address line repair in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A thin film electronic imager device 100, such as a solid stateradiation imager array, typically comprises a plurality of pixels 110arranged in a matrix of rows and columns (a representative one of whichis illustrated in FIG. 1). Pixels in the array are coupled to addresslines which include rows of scan lines 115 and columns of data lines 120via a thin film field effect switching transistor 130 (referred to as a"TFT" or a "FET") such that the charge accumulated by the photosensor ineach pixel can be selectively read out during imager operations. Eachswitching transistor comprises a gate electrode 132 coupled to arespective scan line 115, a drain electrode 134 coupled to a pixelelectrode 112; and a source electrode 136 that is coupled to arespective data line 120 (the nomenclature for source and drainelectrode 134, 136 is not of critical significance in this structure andthus the nomenclature for the respective electrodes 134, 136 can bereversed without affecting the operation or structure of imager array100).

FIG. 1 illustrates imager array 100 at an interim step in thefabrication process known as the "FET complete" step. At this point inthe fabrication process imager array comprises layers of conductive,semiconductive, and dielectric material that are respectively arrangedto form scan lines 115, data lines 120, FETs 130, and pixel electrodes112; in the typical fabrication process, the next step in the formationof silicon photosensor bodies on pixel electrode 112 and the depositionof multiple layers of organic and inorganic dielectric material to formbarriers to protect the photosensors, after which a common electrode isformed over the photosensors and scintillator material is disposed overthe common electrode on the array. Often imager fabrication processes donot provide for repair of defects in address lines until afterphotosensors and barrier layers have been formed; repair at this stagein the fabrication process necessitates removal of barrier layermaterial from the region of the address line defect prior to being ableto repair the defect.

In accordance with this invention, repair of defects in address datalines 120 is accomplished at the "FET complete" stage of the fabricationprocess. At this point in the fabrication process the electricalcontinuity of the address lines can be determined and defects located.Defects may include open circuits in spots where the conductive materialforming the address line is not continuous, or short circuits, which maynecessitate cutting the line, removing the shorted portion, and thenreconnecting the severed portions of respective address lines withproper electrical isolation maintained. In either event, it is notuncommon that open circuit conditions in address lines must becorrected. Open circuits in data lines are particularly critical insingle contact data lines, that is, data lines which are intentionallysevered in the middle of the array to reduce noise in the readout, suchthat each data line segment, with attached pixels, is coupled to readoutelectronics at only one edge of the array. At the FET complete stage ofthe fabrication process, the electrical continuity of address lines canbe determined and defects identified.

A portion of address line 120 having a defect 140 is illustrated incross section in FIG. 2. At the FET complete stage of the fabricationprocess a gate dielectric layer 117 is disposed on a substrate 105; gatedielectric layer comprises a dielectric material, such as silicon oxide(SiOx) or silicon nitride (SiNx), that is disposed over array 100 toelectrical insulate scan lines 115 and insulate associated gateelectrodes 132 from succeeding layers of semiconductive and conductivematerials (not shown) in TFT 130. Data line 120 is disposed on gatedielectric layer 117 and typically comprises a conductive material suchas molybdenum, titanium, aluminum and chromium, or the like. Data line120 typically has a thickness in the range between about 0.2 μm and 1μm.

In accordance with this invention, repair of defect 140 is can becommenced once the location of defect 140 has been identified (e.g., byelectrical tests and visual inspection). Typically the exposed surfaceof array 100 (as used herein, the term "exposed surface" refers to thesurface of the array opposite substrate 105 as it exists at that pointin the fabrication process) is cleaned by applying photoresist stripperor the like to the array. A first protective layer 150 is then depositedin a spin process, meniscus coat process, or the like, over the surfaceof the array; first protective layer 150 typically comprises aninsulative material that can be removed with laser ablation. Forexample, first protective layer comprises photoresist, polyimide, orsimilar materials. As used herein, the term "deposited", "formed" or thelike used with respect to the formation of a layer of material over thearray includes all steps necessary to the formation of such a layer,such as the placement of the material on the array and further normalprocessing of such material to make it a layer, such as curing thematerial placed over the array, or the like. The thickness of firstprotective layer 150 is typically in the range between about 1 μm andabout 4 μm, and commonly has a thickness of about 2 μm.

Next, a repair area 145 (FIG. 2) is formed to expose defect 140, a firstaddress line portion 121, and a second address line portion 122 thatadjoin defect 140. Typically, portions of first protective layer 150disposed over repair area 145 are removed by laser ablation to exposedefect 140 and adjoining address line segments 121, 122. For example, aFlorod brand Model LCM 308 excimer laser has been used at about 7% power(total power being about 350 microjoules) to ablate non-conductivematerial to form repair area 145 having dimensions of about 10 μm by 20μm (width, depth, etc.). First and second address line segments 121, 122collectively comprise areas on each portion of data address lineadjoining by open circuit defect 145. Segments 121 and 122 aresufficiently large to allow subsequently deposited conductive material(as discussed below) to make satisfactory electrical contact to dataline 120 and to form a stable structure. For example, in a typicalimager in which address line 140 has a width of about 7 μm, segments 143and 144 each have a length of about 10 μm. Additionally, sidewalls 155of first protective layer 150 are typically also substantially planar(that is, relatively smooth surfaces that are typically disposedsubstantially vertically between the bottom surface of selected repairarea 145 and the upper surface of first protective layer 150). At thecompletion of this step, repair area 145 is formed with first protectivelayer 150 surrounding the repair area on the exposed surface of array100.

Next, a conductive repair material layer 160 is deposited over array100, typically in a plasma enhanced chemical vapor deposition process orthe like, such that the conductive repair material is disposed over thearray surface, and a portion of the conductive repair material isdisposed in repair area 145 so as to form a repair shunt 165 thatelectrically couples first data address line segment 121 to second dataaddress line segment 122. Conductive repair material layer comprises thesame type of conductive material that comprises data line 120, oralternatively a different type of conductive material. For example,conductive repair material may comprise a metal such as molybdenum,titanium, aluminum, chromium, or the like, or alternatively metal oxidecombinations, such as indium tin oxide or the like. Conductive repairmaterial is typically selected to provide a low bulk resistance (e.g.,about 100 ohms per square or less) so as to reduce electrical noise inthe repaired data line, and such that repair shunt 165 is robust, thatis, provides a connection that is electrically and physically sound andthat withstands the subsequent fabrication steps to complete that array.Conductive repair material layer 160 typically has a thickness in therange between about 0.8μm and 1.2 μm.

Following deposition of conductive repair material layer 160, aplanarized second protective layer 170 is formed over array 100. Secondprotective layer 170 is deposited in a spin process, meniscus coatprocess, or the like, over the surface of the array that results in theupper surface of second protective layer having a planarized surface,that is, a surface that is substantially parallel to the surface ofsubstrate 105. Second protective layer 170 typically comprises aninsulative material that can be removed with laser ablation (e.g.,similar to the material comprising first protective layer 150). Forexample, second protective layer comprises photoresist, polyimide, orsimilar materials. The thickness of second protective layer 170 istypically in the range between about 1 μm and 4 μm, and commonly has athickness of about 2 μm in the region outside of repair area 165 (due tothe planarized surface, the thickness of second protective layer isgreater in repair area 165). At the completion of the formation ofplanarized second protective layer 170 array 100 appears as illustratedin FIG. 3.

Portions of second protective layer 170 are then removed so as to form aplanarized intermediate surface 168 on array 100 in which conductiverepair material layer 160 is exposed (that is, constitutes the uppersurface of array 100 at this stage in the process) except for a repairarea plug portion 175 disposed over repair area 145. Formation ofplanarized intermediate surface 168 is accomplished by, for example, aplanarized etching process such as oxygen plasma etching device, such asa parallel plate asher or the like. The etch is continued until thesurface of conductive repair material 160 is exposed except in repairarea 145; protective plug 175 remains disposed over repair shunt 165. Atthe completion of this step of the process, imager array 100 appears asis illustrated in FIG. 4.

Next, the exposed portions of conductive repair layer 160 are removedfrom array 100, for example by etching with a batch wet etch process.This etching is continued until all exposed portions of conductiverepair material layer 160 are removed from the array, with only repairshunt 165 remaining as it is disposed under and protected from theetching process by protective plug 175. After removal of exposedportions of conductive repair material layer 160, first protective layer150 (outside of repair area 145) and protective plug 175 remain disposedon the array and form the upper surface of the array at this point inthe repair process.

To complete the repair process, remaining portions of first protectivelayer 150 and protective plug 175 are then removed from the array, forexample in an oxygen plasma etching process as described above withrespect to removal of portions of second protective layer 170. Therepaired array appears as illustrated in FIG. 5, with an operation dataaddress line 120 having repair shunt 165. At this point, tests can beperformed to confirm the electrical integrity of the array (withadditional repairs performed as necessary) and fabrication of array 100can proceed with formation of photosensors, barrier layers, commonelectrode, and scintillator (not shown).

The repair process of the present invention thus provides a repair of adata line that can use a wide variety of conductive repair materials,enabling selection of a conductive material that offers low resistanceand can provide a low noise repair. If the repair effort is notsuccessful for any reason, it can readily be repeated without adverseeffects on other parts of the array, thus providing essentially 100%data line repair yield. Further, given the repair process of thisinvention, because the repair is effected at the FET complete stage ofthe array fabrication process, repair shunt 165 is covered by materialsdeposited on the array in subsequent fabrication steps (as the normaldata line is), providing additional protection of repair shunt 165 andmaking the repair more robust than repair schemes accomplished at laterarray fabrication stages. This structure also reduces the possibility ofelectrical leakage between the repair line and subsequently-depositedconductive components in the array. The low-noise data address linerepair method of the present invention thus provides high yield and highquality thin film electronic imagers.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

What is claimed is:
 1. A method of repairing an open circuit defect in adamaged address line in a thin film electronic imager array at an arrayfabrication step prior to deposition of photosensor barrier layers, themethod comprising the steps of:depositing a first protective layer oversaid array; forming a repair area exposing said open circuit defect andportions of said address line adjoining said open circuit defect byablating portions of said first protective layer disposed over saidrepair area to expose said open circuit defect and portions of saidaddress line adjoining said open circuit defect; depositing a layer ofconductive repair material over said array, a portion of the conductiverepair material layer being disposed in said repair area so as to form arepair shunt repair shunt disposed in electrical contact with saiddamaged address line portions adjoining said defect so as toelectrically bridge said defect; forming a planarized second protectivelayer over said array; removing portions of said planarized secondprotective layer to form a planarized surface on said array on whichsaid conductive repair material is exposed except for a plug portion ofsaid second protective layer disposed over said repair area; removingsaid conductive repair material from said array surface except forrepair shunt underlying the second protective layer plug portion; andremoving said remaining portions of said first protective layer and saidsecond protective layer plug portion from said array.
 2. The method ofclaim 1 wherein said first protective layer comprises an insulatingmaterial selected from the group consisting of photoresist material andpolyimide insulation material.
 3. The method of claim 2 wherein saidfirst protective layer is deposited to a thickness in the range between1 μm and 4 μm.
 4. The method of claim 1 wherein said damaged addressline comprises a conductive material and said conductive repair materialcomprises the same type of conductive material as comprises said damagedaddress line.
 5. The method of claim 1 wherein said damaged address linecomprises a conductive material and said conductive repair materialcomprises the different type of conductive material as comprises saiddamaged address line.
 6. The method of claim 1 wherein said planarizedsecond protective layer comprises an insulating material selected fromthe group consisting of photoresist material and polyimide insulationmaterial.
 7. The method of claim 1 wherein the step of removing portionsof said second protective layer to form a planarized surface on saidarray exposing said conductive repair material except for said plugportion comprises the step of etching said second protective layer in anoxygen plasma.
 8. The method of claim 1 wherein the step of removing theconductive repair material exposed after removal of said secondprotective layer comprises the step of etching said conductive repairmaterial in an etchant selective to the second protective layer materialcomprising said plug portion.
 9. The method of claim 1 wherein the stepof removing remaining portions of said first protective layer and saidsecond plug portion comprises etching said array in an oxygen plasma.10. The method of claim 1 wherein said address line comprises a materialselected from the group consisting of molybdenum, titanium, aluminum andchromium.